Electrical resistance heater assemblies for heating pipes are generally known in the art and have been employed for a long period of time. These heated assemblies are disposed externally on the pipes containing the material to be heated. Heretofore, in order to improve the heat transfer from the heater element to the pipe the prior art has generally employed one of two methods. That is, the heater has been installed parallel to the pipe or spiraled around the pipe and then attached to the pipe at approximately one foot intervals by bands. In such a method contact between the heater and the pipe is assured only under the bands and thermal expansion results in air space between the heater and the pipe where the bands do not force the heater to remain in contact with the pipe. Moreover, such bands often result in localized excessive pressure causing mechanical damage to the heater elements.
In another method the heater is enclosed in a cover filled with heat transfer cement generally of a graphite base. Either the cover is preformed with the heat transfer cement situated therein in a putty-like or plastic state as shown for example in U.S. Pat. No. 3,331,946 or the heat transfer cement or material is preshaped or extruded around the heater to conform closely to the inner cavity surface of the cover member and also the other surface of the cement or material is preshaped or extruded to conform closely to the shape of the pipe surface on which it is mounted, as shown for example in U.S. Pat. No. 3,834,458 and 3,949,189. While this latter method is designed to eliminate the undesirable air gaps between the heater and the pipe and to improve the conductance of heat between the heater element and the pipe it has been found that the efficiency of such a system still depends too heavily upon the personnel handling and installing the putty-like heat transfer cement or material and that although the elimination of air gaps was desired this elimination has not been dependably obtained. Furthermore, the handling or use of such heat transfer cement or material is both cumbersome and expensive.